Pulp molded articles have been extending their use, taking the place of plastic molded articles from the environmental considerations. Pulp molded articles are produced by, for example, a method including a papermaking step in which a pulp slurry is fed to the papermaking side of a papermaking mold having a plurality of holes and sucked through the holes to accumulate pulp on the papermaking side to form a wet preform, a dewatering step in which the wet preform as molded in the papermaking step is dewatered, and a drying step in which the dewatered and yet undried preform as obtained in the dewatering step is put into a drying mold and press-dried. It is desirable for the molded article thus prepared to have narrow ridges on its outer side which will function as nonslip or reinforcing ribs to provide ease of handling and shape retention. A technique for forming ridges on the surface of a pulp molded article is disclosed in JP-A-9-132900. According to this technique, a papermaking mold having narrow grooves is used to form ridges corresponding to the grooves on the surface of a molded article in the papermaking step.
Where ridges are formed on the surface of a molded article during papermaking as in the above-described technique, a dewatering mold or a drying mold used in the subsequent dewatering or drying step must have narrow grooves of slit form corresponding to the ridges. Besides, the ridges must be accurately fitted into the grooves so as not to deform the wet and therefore easily deformable preform as obtained by papermaking, especially the exterior ridges thereof. Such registration is extremely difficult. JP-A-6-158599 discloses a technique in which a drying mold having core vents for steam escape passage is used to increase drying efficiency. The drying mold proposed is incapable of forming narrow ridges. That is, because projections are apt to trap steam during drying and cause so-called steam explosion, it has been difficult to form projections having a high density up to their tips (apices).